(1) Field of the Invention
The present invention relates to a method and apparatus for detection of volatile products in a sample using transducers which change resistance as a function of contact of the volatile products from the sample. In particular, the present invention relates to a method for detecting spoilage or microorganisms, particularly pathogenic microorganisms, in a sample.
(2) Description of Related Art
Food safety concerns are currently impacting public health, the meat industry, and animal production agriculture. Animal agriculture has been under increasing scrutiny as a source of foodborne pathogens. There is a need to develop a new technology that can be applied to pre-harvest food safety efforts, particularly for identifying and monitoring a potential human pathogen xe2x80x9con the farmxe2x80x9d.
Escherichia coli (E. coli) O157:H7 has been recognized as a significant bacterial pathogen belonging to a group of enterohemorrhagic E. coli associated with bloody diarrhea. It is important public health concern because of its association with commonly consumed foods, such as ground beef. Infection with this organism can cause hemorrhagic colitis, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura. The association of E. coli O157:H7 with ground beef has led to the identification of cattle as a reservoir for the organism. Recent pre-harvest food safety efforts have emphasized identifying factors within cattle production systems for the monitoring and control of E. coli O157:H7.
Computer controlled gas sensor based instruments, referred to as artificial olfactory or electronic nose technology, are finding increasing application in the food industry. The sensors are designed to detect volatile compounds that result from spoilage, rancidity, or other xe2x80x9coffxe2x80x9d odors. Promising results have been shown when this technology was applied to differentiating between different species of bacteria and spoilage fungi.
In today""s farming industry, potatoes are stored in large bins before they are shipped out to their various destinations. Disease during storage is magnified due to extended storage periods and by requiring higher storage temperatures for immediate processing of the potatoes (Varns and Glynn, 1979). Disease losses of potatoes in storage may be as high as 30% (The Grower, 1980). As potato processing contributes up to two billion dollars a year to the economy, a small percentage of disease losses represent a significant cost to the potato industry. Currently, the managers of the potato bins monitor odor and wetness at the bottom of the bin to determine rot. By the time these indicators are detected, economic losses can be significant. At the moment, nothing can be done to arrest the spread of the damage. Monitoring of volatiles arising from host-pathogen interactions could become an important early warning of potato disease problems. Disease due to Erwinia carotovora infection is a major problem in potato storage. Erwinia carotovora is a facultative anaerobic organism, in which the bacterium breaks down the structure of the vegetative cells of infected potatoes, causing soft rot. This causes a layer of wet slime to form on the outside of the potato, resulting in anaerobic conditions in the underlying cells (Costa and Loper, 1994). Varns and Glynn (1979) reported that potatoes infected with the bacterium Erwinia carotovora showed high levels of acetone, ethanol, and 2-butanone. Additional volatiles included acetaldehyde, methyl acetate, ethyl acetate, propanethiol, hydrogen sulfide, methyl sulfide, methyl disulfide, n-propanol, and isobutanol (Varns and Glynn, 1979). Waterer and Pritchard (1984) reported methanol, acetaldehyde, ethanol, 2-propanol, acetone, 1-propanol, and 1-butanol in the headspace of E. carotovora var. carotovora infected Russet Burbank potato tubers. These volatiles can be produced from intermediates as well as the end-product (pyruvate) of the Embden-Meyerhof pathway (Metzler, 1977).
The sense of smell has long been used as a diagnostic tool by medical professionals, law enforcement, food handlers, and countless others in everyday life. The human nose contains approximately 50 million cells in the olfactory epithelium that act as primary receptors to odorous molecules (Gardner et a., 1990; Vandendorpe, 1998). This parallel architecture led to the construction of the electronic nose, which mimics the biological system. The electronic nose is a state-of-the-art technology that can be used to provide rapid and continuous monitoring of a wide array of different volatile compounds. The term xe2x80x9celectronic nosexe2x80x9d is applied to an array of chemical sensors, where each sensor has only partial specificity to a wide range of odorant molecules (Bartless et al., 1997). By mapping the sensitivity of the sensors to different chemicals, a complex odor can be xe2x80x9cfingerprintedxe2x80x9d and identified (Lipman, 1998). The primary receptors in the biological system are replaced by an array of transducers, such as metal oxide films, that respond to a broad range of chemical vapors or odors. Electronic nose instrumentation has advanced rapidly during the past ten years, the majority of application being within the food and drink industries (Gardner and Bartlett, 1992; Kress-Rogers, 1997). Research is being done on the applications of the electronic nose in human healthcare, particularly in the identification of infection (Doctor""s Guide to Medical and Other News. xe2x80x9cElectronic Nose Sniffs out Infectionxe2x80x9d). The instrument has also been successfully applied to detect vapors (Gardner et al., 1990; Keller et al., 1994) and aviation fuels (Lauf and Hoffheins, 1990). Application in microbial detection has been reported for Clostridium perfringes, Proteus, Haemophilus influenzae, Bacteriodes fragilis, Oxford staphylococcus, Pseudomonas aeruginosa (craven et a., 1994), Staphylococcus aureus, and E. coli (Gardner et al., 1998). U.S. Pat. No. 5,807,701 to Payne et al and U.S. Pat. No. 6,017,440 to Lewis et al describe apparatus for detecting microorganisms. These patents describe different types of sensors (transducers). These methods use an array of sensors for detection.
The present invention relates to an apparatus for detection of a volatile product in a sample which comprises: a circuit comprising a transducer means mounted in a confined space for containing the sample which detects the volatile product produced from the sample to produce an analog signal; an analog to digital conversion means in the circuit for converting the analog signal to a digital signal; and acquisition means in the circuit which stores the digital signal resulting from the analog signal, in memory as a detectable signal and retrieves the detectable signal to provide the detection of the volatile product wherein the volatile product in the confined space is detected over time to produce a distinctive signature. The present invention is particularly used to detect pathogenic E. coli and salmonella sp.
Further, the present invention relates to a method for detecting a volatile product in a sample providing an apparatus adjacent the sample which comprises: a circuit comprising a transducer means mounted in the confined space for containing the sample which detects the volatile product produced from the sample to produce an analog signal; an analog to digital conversion means in the circuit for converting the analog signal to a digital signal; an acquisition means in the circuit which stores the digital signal resulting from the analog signal in a memory as a detectable signal and retrieves the detectable signal to provide detection of the volatile product; and detecting the product in the sample with the transducer means in the circuit wherein the volatile product in the confined space is detected over time to produce a distinctive signature.
Further, the present invention relates to an apparatus for the detection of a volatile by-product produced by a microorganism as a result of spoilage of a food material which comprises: a circuit comprising a transducer means mounted in a confined space containing a sample of the food material which detects the by-product produced by the microorganism to produce an analog signal; an analog to digital converter means in the circuit for converting the analog signal to a digital signal; and acquisition means in the circuit which stores from the digital signal resulting from the analog signal in a memory as a detectable signal, and retrieves the detectable signal to produce the detection of the volatile by-product wherein the volatile by-product is detected over time to produce a distinctive signature.
Further, the present invention relates to a method for detecting a volatile by-product produced by a microorganism as a result of spoilage of a biological material which comprises: providing an apparatus for the detection of a volatile by-product produced by a microorganism which comprises: a circuit comprising a transducer means mounted in a container for containing the sample which detects the by-product produced by the microorganism to produce an analog signal; an analog to digital converter means in the circuit for converting the analog signal to a digital signal; and acquisition means in the circuit which stores the digital signal resulting from the analog signal in memory as a detectable signal and retrieves the detectable signal to provide the detection of the by-product; and detecting the volatile by-product of the microorganism with the transducer means in the circuit, wherein the volatile by-product in the confined space is detected over time to produce a distinctive signature.
It is therefore an object of the present invention to provide an apparatus and method for the detection of very small amounts of a volatile product (less than 10xe2x88x921) parts of a volatile material per part by volume of an atmosphere around a sample. In particular, the present invention provides a detecting apparatus which uses artificial intelligence in the form of a neural network to detect a signature showing the presence of the volatile material in a sample. Further still, it is an object of the present invention to provide an apparatus and method for the detection of harmful microorganisms by measuring volatile products produced by the microorganism. Further, it is an object of the present invention to provide an apparatus and method for the detection of spoilage by-products produced by microorganisms or degradative oxidation in foods and other biological materials.
These and other objects will become increasingly apparent by reference to the following description and the drawings.